My view is why would you want to remove the phosphate coating as it is a reasonably good anti-corrosion coating anyway? The only reason why you would want to do so is if the phosphate coating has broken down and there is rust or corrosion on the part. If the phosphate coating is good then I would detail the part using a primer and then some good paint.
If you strip the phosphate coating the part will have to be repainted anyway as it will begin to look untidy in a very short time. Natural parts are great, I have a lot of the on my car but the six weeks worth of re-detailing parts every year gets a bit tedious after a while.
Cheers, Brad.